A conventional image display device fails to adjust a display luminance so sufficiently that the adjustment is suitable for human visual properties, particularly, for human optic adaptability to brightness. Specifically, a conventional image display device fails to adjust a display luminance so that the adjustment corresponds to a photoenvironment of an image display device, i.e., the adjustment corresponds to brightness around the image display device.
This raises such problem that the user feels “too bright” or feels “black is not sufficiently deep (black loses its depth)” or does not feel any “radiance”.
The user feels “too bright” when the user views a bright display in case where a periphery of the image display device is dark for example. This is because human is likely to feel brightness when a periphery thereof is dark. Further, the user feels “black loses its depth” when the user views a dark display in case where the periphery is dark.
On the other hand, the user does not feel “radiance” when the user views a bright display, for example, in case where the periphery of the image display device is bright. This is because human is unlikely to feel brightness when the periphery is bright.
Thus, in order to solve the foregoing problems, there has been proposed a technique in which brightness of an image to be displayed is adjusted in accordance with brightness of the periphery of the image display device.
For example, Patent Literature 1 describes a transmission type liquid crystal display element configured so that a luminance of an image to be displayed is adjusted in accordance with brightness of a periphery of the transmission type liquid crystal display element. FIG. 11 is a diagram illustrating essential portions of a conventional transmission type liquid crystal display element 100 described in Patent Literature 1. As illustrated in FIG. 11, the transmission type liquid crystal display element 100 includes a light receiving element 110, and the light receiving element 110 collects information on brightness of the periphery. Further, the thus collected information is amplified by a signal amplification circuit 120 as a signal and is transmitted to a display controller 130 and a power supply circuit 140.
The display controller 130 having received the signal changes a voltage added to a liquid crystal layer in accordance with content of the signal so as to change brightness of an image. In response to the signal, the power supply circuit 140 changes brightness of a light source 150 in accordance with the content of the signal. The display controller 130 and the power supply circuit 140 act to adjust a luminance of an image on a display screen according to brightness of the periphery.